The present invention relates to charge-beam exposure in lithography for semiconductor device manufacture.
An optical stepper with superior productivity has been used at the mass production stage of semiconductor memory device manufacture. For the production of memory devices from 1 GDRAM and 4 GDRAM downward having a line width of 0.2 xcexcm or less, an electron-beam exposure method having a high resolution and superior in productivity is expected as one of exposure arts suitable for an optical exposure method.
Conventional electron-beam exposure methods mainly use a single-light-beam Gaussian method and a variable forming method. However, because these methods are inferior in productivity, they have been used for such purposes making good use of a superior resolution characteristic of the electron beam as mask drawing, research and development of VLSIs, and exposure of ASIC devices according to small-scale production.
Thus, to apply the electron beam exposure method to mass production, how to improve the productivity is a large problem. In the case of a conventional electron-beam aligner, however, an exposure area of an electronic optical system that can be exposed through one shot is extremely small compared to an exposure area of a projection optical system of an optical aligner. Therefore, to expose a wafer, because electronic and mechanical scanning distances increase compared to those of an optical aligner, a lot of time is required and throughput is extremely lowered. To improve the throughput, it is necessary to greatly accelerate electronic scanning and mechanical scanning or expand an exposure area for one shot.
To improve the throughput while keeping a necessary resolution, a method of forming a circuit pattern to be exposed on a silicon wafer as a mask, applying an electron beam whose exposure area is expanded to the mask, and transferring the mask pattern onto the wafer is studied. An electron-beam mask used for an electron-beam aligner usually has a circuit pattern 2 to 5 times larger than a circuit pattern on a silicon wafer, depending on a projection-system magnification of an electron-beam aligner. For example, it is said that a circuit pattern of one chip of a 4 Gbit-DRAM requires an area of approx. 20 mmxc3x9735 mm. A circuit pattern area on a mask for exposing the circuit pattern requires 80 mmxc3x97140 mm when a projection-system magnification is xc2xc. As shown in FIG. 26A, it is difficult to form a chip pattern (thin film portion) 600 having the above size enclosed by a beam portion 601 in a thin-film window on a mask 602 at a high-enough strength and accuracy. Therefore, as schematically shown in FIG. 26B, a structure is used in which the chip pattern 600 is divided into a plurality of portions and a reinforcement beam 603 is set between divided patterns.
FIG. 27A shows a perspective view of an example of the above electron-beam mask and FIG. 27B shows a sectional view of the mask.
A plurality of mask pattern areas 501 are formed on a mask substrate 502 fixed onto a mask stage 506 and a portion between mask pattern areas 501 is reinforced by a reinforcement beam 505.
The mask pattern area 501 is formed by patterning an electron-beam scatterer (high scatterer) 504 having a W of 0.02 xcexcm on an electron-beam passing film (low scatterer) 503 (FIG. 27B) serving as a membrane made of SiN having a thickness of 0.15 xcexcgm formed on the mask substrate 502 of a silicon wafer having a thickness of, for example, 2 mm. Because it is difficult to handle the silicon wafer alone, it is fixed to a mask stage 506 used for X-ray exposure.
FIG. 28 shows an example of a conventional transfer system for transferring divided mask patterns.
An electron beam 510 emitted from an electron source 501 is converged by a first condenser lens 511 and shaped into a rectangular electron beam by a forming aperture 502. The shaped electron beam 510 is formed into an almost parallel electron beam by a second condenser lens 512 and applied to a mask 505. The mask 505 is mounted on a mask stage 506 and continuously moved together with the mask stage 506 (this movement direction is assumed to be the x direction). The electron beam 510 passing through the mask 505 is contracted and transferred to a wafer 508 mounted on a wafer stage 509 continuously moving in the opposite direction to the mask stage 506 by a first projection lens 513 and a second projection lens 514.
FIG. 29 shows how divided chip patterns on the mask 505 are transferred onto the wafer 508.
The mask stage 506 moves from the electron beam 510 stopping under exposure along an arrow E shown at the top right in FIG. 29. A group of divided chip patterns on the mask 505 to which the electron beam 510 is applied due to one-time movement of the mask stage 506 in the X direction is referred to as a divided chip pattern on a stripe. For example, divided chip patterns M11, M12, . . . , and M16 are present on the same stripe.
Moreover, the mask stage 506 and wafer stage 509 move synchronously each other. The wafer stage 509 is moved along an arrow Fat the bottom right in FIG. 29. Furthermore, patterns between stripes are connected so that beams between stripes on the mask 505 do not appear on contracted patterns on the wafer stage 508 by moving the mask stage 506 and wafer stage 509 to the first pattern of each stripe. Patterns M11, M12 . . . on the mask 505 are contracted on the wafer 508 and transferred as W11, W12 . . . .
FIGS. 30A to 30E show states of transferring a divided pattern M26 and a divided pattern M25 on the mask 505 having a beam width S56 in FIG. 29.
In FIGS. 30A to 30E, symbol B denotes a light beam, BA denotes a light-beam optical axis, an arrow M denotes a moving direction of a mask, and an arrow denotes a moving direction of a wafer, and the arrow M and arrow W show directions opposite to each other.
Exposure of the divided pattern M26 onto the wafer 508 is started (FIG. 30A) and the divided pattern M26 is exposed onto the wafer 508 as a divided pattern W26 to be transferred in accordance with the relative movement between the mask 505 and the wafer 508 (FIG. 30B) When every divided pattern M26 is exposed on the wafer 508 as the divided pattern W26 to be transferred, exposure of the divided pattern M26 is completed (FIG. 30C). Then, exposure of the divided pattern M25 onto the wafer 508 is started as a divided pattern W25 to be transferred (FIG. 30D) and exposure of the next divided pattern M25 is exposed similarly to the exposure of the divided pattern M26 (FIG. 30E).
However, the above transfer method has the following problem.
That is, as clarified from the description about the illustration of the chip 3 on the wafer 508 in FIG. 29 and FIGS. 30A to 30E, beams shown by s12, s23, s34, s45, and s56 in FIG. 29 present between divided patterns on the same stripe on the mask 505 are left on the wafer 508 as gaps shown by SW12, SW23, SW34, SW45, and SW56, all divided patterns are connected, and thereby a transferred pattern shown in FIG. 31 necessary for a chip pattern circuit to normally operate cannot be realized.
To solve the above problem, a method of repeatedly stopping and moving a wafer stage depending on a light-beam position on a mask while continuously moving a mask stage is considered. This is a method of moving a wafer stage when a light beam is present on a divided pattern on a mask on the same stripe but stopping the wafer stage when the light beam is present on a beam portion between divided patterns to remove the gaps s12, s23, s34, s45, and s56 from a wafer. According to the above method, it may be possible to connect divided patterns on a wafer as shown in FIG. 31. However, it is very difficult to practically use the above method because in the case of the mechanical connection control, a pattern connection accuracy is lowered due to vibration generated when a stage is accelerated or decelerated or deterioration of a pattern connection accuracy arises due to a low mechanical control response speed.
Therefore, it is an object of the present invention to provide a mask pattern transfer method for accurately connecting divided patterns on a mask on a wafer, a mask pattern transfer apparatus using the mask pattern transfer method, and a device manufacturing method.
To attain the above object, the present invention uses a mask pattern transfer method for transferring a desired pattern onto an object with a charged beam by using a mask on which divided patterns obtained by dividing the desired pattern are arranged, comprising:
a step of continuously moving the object and the mask relative to the charged beam in a direction along which a first divided pattern and a second divided pattern adjacent to the first divided pattern are arranged; and
a step of deflecting the charged beam passed through the mask so that a first exposure area in which the first divided pattern is exposed and a second exposure area in which the second divided pattern is exposed are connected to each other.
As described above, in the case of a mask pattern transfer method of the present invention, a mask and an object continuously and relatively move, thereby vibration due to acceleration/deceleration of the mask and object or a low mechanical control response speed is removed, and thus a pattern connection accuracy is not lowered.
Moreover, because deflection of a charged beam passing through divided patterns is set, a desired pattern is obtained by setting the deflection for connecting divided patterns on a mask arranged at both sides of a beam on an object.
In the case of a mask pattern method of the present invention, it is permitted that a deflection value of a charged beam passing through divided patterns is not accumulated. In this case, because an error about a position is prevented from occurring at the time that exposure is successively performed, the method is preferable at the time of exposing a pattern to be divided into many sub-patterns.
The present invention also provides mask pattern transfer apparatus for transferring a desired pattern onto an object with a charged beam by using a mask on which divided patterns obtained by dividing the desired pattern are arranged, the apparatus comprising:
a beam generator which generates the charged beam toward the mask;
a movable mask stage on which the mask is mounted;
a movable object stage on which the object is mounted;
a first deflector which continuously deflects the charged beam passed through the mask; and
a controller for continuously moving the mask stage and the object stage from a start of exposure of a first exposure area in which a first divided pattern is exposed up to an end of exposure of a second exposure area in which a second divided pattern is exposed, and after exposing the first exposure area, making the first deflector deflect the charged beam in a continuous moving direction of the object.
A device manufacturing method of the present invention includes the step of transferring a mask pattern by using the above mask pattern transfer method.
A device manufacturing method of the present invention includes the step of transferring a mask pattern by using the above mask pattern transfer apparatus.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.